Temperature, particle motion, and how much the temperature changes

Answer Key - Grade 8 Science Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.

1. 1.

   The mug stands on a table. Ari's tea cools in a mug. By how many °C does it cool from minute 2 to minute 10?

   28 °C
2. 2.

   The cup has no lid. Esme's cocoa cools in a cup. By how many °C does it cool from minute 4 to minute 12?

   17 °C

3. Read this first

   Water in a mug and in a bathtub (example data)

   container	mass of water (g)	temperature (°C)
   Mug	250	40
   Bathtub	80000	40

4. 3.

   Jun compares a mug of water and a full bathtub of water. Which statement does the table support?

   • The bathtub is at the higher temperature, since it holds so much more thermal energy than the mug does
   • The temperatures match, so the particles move equally fast on average, but the bathtub holds more thermal energy
   • The mug is at the higher temperature, since its particles are packed into a much smaller space than the tub's
   • The mug and the bathtub hold equal thermal energy, since they are at the same temperature as each other

5. Two cups of water (example data)

   cup	mass of water (g)	temperature (°C)
   X	200	80
   Y	200	40

6. 4.

   Cup X and cup Y hold the same mass of water. Which statement does the table support, Kira?

   • Cup X has faster particles on average, and with equal mass it also holds more thermal energy
   • The cups hold equal thermal energy, since temperature and thermal energy are the same measure
   • Cup Y has faster particles on average, since cooler water gives its particles more room to move
   • Cup X is at the higher temperature because it has more particles than cup Y, which makes it hotter

7. A small cup and a large cup of water (example data)

   cup	mass of water (g)	temperature (°C)
   Small	100	90
   Large	1000	30

8. 5.

   Luz compares two cups of water. Which statement does the table support?

   • The two cups are at the same temperature, since 100 g at 90 °C balances 1000 g at 30 °C
   • The small cup's particles move faster on average, while the large cup holds more total thermal energy
   • The large cup's particles move faster on average, since it holds more total thermal energy than the small cup
   • The small cup holds more thermal energy than the large cup, since it is at the higher temperature
9. 6.

   A thermometer in a pot of water reads 20 °C, then 35 °C after heating. What changed in the water's particles, Milo?

   • On average they kept the same speed, but they spread farther apart in the pot
   • On average they moved the same speed, but more of them were moving than before
   • On average they move faster, but they keep the same size and the same number
   • On average they grew larger, and larger particles show up as a higher temperature
10. 7.

    A hot drink cools from 80 °C to 40 °C. What happens to its particles, Noah?

    • They move faster but spread out into the room, so the drink holds less thermal energy
    • On average they move slower, and the drink holds less thermal energy than before
    • They shrink as the drink cools, so the drink holds less thermal energy than before
    • Half of them stop moving, and the rest keep their original speed as the drink cools
11. 8.

    The same heater gives each beaker the same energy. Ren heats two beakers with the same amount of energy. Which one warms by more degrees, and why?

    • Beaker A, since the same energy is shared among fewer particles
    • Beaker B, since it holds more particles to take in the energy from the heater
    • Beaker B, since a larger beaker traps the energy from the heater better than a smaller one
    • The two beakers rise by equal amounts, since the heater gives each of them equal energy

12. Energy to warm 1 g by 1 °C (rounded values)

    material	energy (J)
    Water	4.2
    Sand	0.84

13. 9.

    Equal masses of sand and water get the same energy. Which warms by more degrees, Tala?

    • The sand warms more, since each gram of sand needs less energy to rise one degree
    • The sand warms more, since each gram of sand needs more energy to rise one degree
    • The water warms more, since a liquid's particles move freely and pick up energy faster
    • The two warm equally, since equal masses are given equal energy by the same heater

14. Two samples (rounded values)

    sample	material	mass (g)	energy to warm 1 g by 1 °C (J)
    P	iron	50	0.45
    Q	water	200	4.2

15. 10.

    Samples P and Q get the same energy. Which one warms by more degrees, Zee?

    • Sample P (iron), since it has less mass and needs less energy per gram per degree
    • Sample Q (water), since it has more mass and so holds more particles to take in the energy
    • Sample Q (water), since liquids heat up faster than solids because their particles slide past each other
    • They warm by equal amounts, since the heater gave each sample the same amount of energy